Some implantable medical devices, such as cardiac monitors, may sense and record cardiac signals of a patient. Example cardiac signals include an electrogram or an electrocardiogram. In some cases, a cardiac monitor may be a part of a device that does not include stimulation capabilities, while in other cases, a cardiac monitor may be incorporated in a device that includes a stimulation generator, which generates and delivers therapy to the patient, such as a pacemaker, cardioverter or defibrillator. Some types of medical devices may only store cardiac signals of interest, such as the signals that exhibit a departure from a normal cardiac signal, e.g., a sinus rhythm.
Cardiac signals recorded by a cardiac monitor may be retrieved and analyzed to diagnose a patient condition, such as syncope or cardiac arrhythmia. For example, a clinician may retrieve the stored cardiac signal data from the implantable device with the aid of an external device that communicates with the implantable device. Syncope and cardiac arrhythmias may be related. For example, syncope may be triggered by a cardiac arrhythmia, such as bradycardia, tachyarrhythmia. However, in some instances, syncope may be unrelated to a cardiac arrhythmia, and may be attributable to, for example, low blood pressure that is not caused by a cardiac arrhythmia.
Syncopic events may occur relatively infrequently and have a relatively short duration and/or a relatively sudden onset. Implantable cardiac monitors may be a useful tool for long-term monitoring of a patient's cardiac signals in order to help diagnose the source of the patient's syncope.